1. Technical Field
The present invention relates to a piezoelectric device having a piezoelectric layer, a MEMS device having a piezoelectric device, a liquid ejecting head, and a liquid ejecting apparatus.
2. Related Art
An example of a piezoelectric element used in a piezoelectric device is a piezoelectric element having a structure in which a piezoelectric material exhibiting an electromechanical conversion function is held between two electrodes, namely, a lower electrode and an upper electrode. Examples of such a piezoelectric material include a piezoelectric layer composed of a crystalline dielectric material. Such a piezoelectric element is generally called as a flexural vibration mode actuator, and used by being mounted on a liquid ejecting head or the like. One of the typical examples of a liquid ejecting head includes an ink jet recording head including a pressure generating chamber which communicates with a nozzle opening for ejecting ink droplets, a part of the pressure generating chamber being formed of a vibrating plate. Ink droplets are ejected from the nozzle opening by deforming the vibrating plate with a piezoelectric element to pressurize the ink in the pressure generating chamber.
As a piezoelectric device used for such as an ink jet recording head, a piezoelectric device having a piezoelectric layer formed of a piezoelectric material and a protective film covering the piezoelectric layer has been proposed (for example, See JP-A-2008-173924 and JP-A-2015-208882).
However, when the piezoelectric layer is covered with the protective film, the protective film disturbs the displacement of the piezoelectric layer. Accordingly, desired displacement characteristics may not be obtained.
Further, when the thickness of the protective film is reduced to suppress the disturbance to the displacement of the piezoelectric layer by the protective film, it may become difficult to fully protect the piezoelectric layer from the environment such as moisture in air by the protective film.
Such problems arise not only in a piezoelectric device used for a liquid ejecting head represented by an ink jet recording head, but also in other piezoelectric devices as well.